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The closest one can come to actually seeing a two dimensional shape is by looking at a paper cut out of one. The paper has thickness, however, so even these shapes are technically three dimensional. Three-dimensional shapes, such as cubes, pyramids and spheres, can be measured in the three dimensions of length, width and depth.

Some two dimensional shapes are known as polygons. A polygon is a shape with three or more straight sides that is closed. Triangles, squares and pentagons are classified as polygons. A polygon cannot have rounded sides, like a square, or intersecting sides, like an hourglass shape. In some instances, however, a circle is considered to be polygon that has an infinite number of sides. A polygon that has equal measurements for all of its sides and angles is known as a regular polygon. Squares and equilateral triangles are examples of regular polygons.

In addition to measuring the sides and angles of two-dimensional objects, its also possible to measure the shapes' perimeter and area. The perimeter is how long all the sides of the shape are when added together. The area represents how much space is inside the shape.

Three-dimensional shapes are solid shapes that exist in three dimensions, which include length, width and depth. The main difference between 3-D shapes and 1-D or 2-D shapes is that depth is incorporated along a third axis outside of the original 2-D plane.

Two-dimensional, or 2-D, shapes are those that exist in only two dimensions while three-dimensional, or 3-D, shapes exist in three dimensions. Both 2-D and 3-D shapes typically have length and width dimensions, also referred to as "x" and "y" dimensions, but 3-D shapes also have a depth dimension in the "z" direction.

Some commonly-known shapes are squares, circles, triangles, stars and rectangles. There are many different kinds of polygons used in geometry and many shapes that combine or arrange multiple polygons to be used in designs.